An absorbent structure for absorbent articles, such as diapers, incontinence protectors and sanitary towels which are intended to be used once and disposed of, is usually made up of one or more sheets of hydrophilic fibres, for example cellulose fluff pulp. Superabsorbents are also often included, which are polymers with an ability to absorb many times their own weight of water or body fluid. In addition, the absorbent structure can also contain further components, for example in order to improve its liquid-spreading properties or to increase its stability and its ability to withstand deformation during use.
An important problem encountered primarily in the case of diapers and incontinence protectors for adults, intended to receive and absorb relatively large amounts of fluid, is that these often leak before their total absorption capacity has been fully utilized. Since, when urinating, large amounts of fluid are often released in the space of a few seconds, this can lead to the absorbent structure being locally saturated with liquid in the liquid-receiving zone, i.e. the liquid does not have time to spread to other parts of the absorbent structure. This means that additional liquid released by the user leaks out of the diaper. This kind of early leakage is of course a source of considerable irritation both for the user and for the person caring for the user. The leakage problem is accentuated upon repeated wetting.
EP 254,476 describes an absorbent structure which, in a zone substantially in front of the wetting area, has a lower weight per unit area and a lower density compared to surrounding portions of the absorbent structure. In this way, a high liquid absorption capacity in the wetting area is achieved, after which the liquid can spread out farther and is stored in the surrounding areas of the absorbent structure.
GB 2,082,643 further describes an absorbent structure with a substantially uniform weight per unit area, but with a density gradient in the longitudinal direction, such that the density increases towards the end portions of the absorbent structure.
U.S. Pat. No. 4,413,996 describes an absorbent structure for diapers which has a liquid-collecting recess or well in the wetting area. A porous wadding can be arranged, if appropriate, in this well.
However, there is still room for improvement as regards the liquid absorption capacity and the spreading ability, in particular in the case of products which are intended to take up large amounts of liquid in a short period of time.